DE 103 00 974 A1 discloses a proportional solenoid valve of a camshaft adjuster device for motor vehicles. The proportional solenoid valve has a valve housing in which a piston is slidable and which has a plurality of ports via which hydraulic oil can be supplied. The proportional solenoid valve also comprises an electromagnet part by means of which the piston can be adjusted via a plunger. The plunger is mounted in an axial bore in a housing of the electromagnet part, whereby it can slide axially.
DE 102 11 467 A1 presents a camshaft adjuster having an electromagnet which is designed as a repelling proportional magnet. The proportional magnet has a magnet armature which is fixedly seated on an armature plunger guided through a pole core and which bears with a free end surface against a control piston or against a part fixedly connected thereto.
DE 101 53 019 A1 presents an electromagnet which is suitable in particular as a proportional magnet for actuating a hydraulic valve. The electromagnet comprises a hollow cylindrical coil body which is delimited by an upper pole shoe and a lower pole shoe. The electromagnet is surrounded by a magnet housing. The coil body acts magnetically on a magnet armature which transmits the magnetic force onward via a plunger rod for actuating the hydraulic valve. The plunger rod is mounted in an axial bore in the lower pole shoe, whereby it can slide axially.
DE 10 2004 057 873 A1 relates to a seat valve having a line system for conducting through an inflowing medium. The seat valve has a seat and an adjustable closing element in the line system. The adjustable closing element is actuated by means of an electromagnetic actuating device. The electromagnetic actuating device comprises an armature housing in which an armature is arranged so as to be adjustable in the direction of a coil axis. The armature is connected to an actuating element which actuates the closing element. The actuating element is mounted in an axial bore in the housing of the electromagnetic actuating device, whereby it can slide axially.
DE 10 2005 048 732 A1 relates to an electromagnetic actuating unit of a hydraulic directional control valve. The electromagnetic actuating unit comprises an armature, which is arranged in an axially slidable manner within an armature chamber, and a pole core, which is arranged in a receptacle and delimits the armature chamber in one movement direction of the armature. Furthermore, the electromagnetic actuating unit comprises a coil which is preferably encapsulated with a non-magnetizable material so as to form a coil body. The armature is mounted in a sliding sleeve, whereby it can slide axially with low friction.
JP 2005-188630 A presents a hydraulic directional control valve having an electromagnetic actuating unit. The electromagnetic actuating unit comprises a coil for generating a magnetic field which acts on an axially slidable armature. The armature comprises an actuating element which actuates the hydraulic directional control valve. The actuating element is mounted in an axial bore in the housing of the electromagnetic actuating device, whereby it can slide axially.
FIG. 1 shows a further electromagnetic actuating unit according to the prior art in a longitudinal sectional illustration. Said electromagnetic actuating unit is designed for actuating a hydraulic directional control valve which is designed as a central valve and which is arranged radially within an inner rotor of a device for variably adjusting the control times of an internal combustion engine. The electromagnetic actuating unit comprises firstly a coil 01 which is fed electrically via a plug contact 02. The coil 01 is arranged within a coil body 03 which is produced by the encapsulation of the coil 01 with a plastic. The magnetic field that can be generated by means of the coil 01 is transmitted via a soft iron circuit, composed of a yoke 04, a yoke plate 06, a pole core 07 and a housing 08, to an axially movably mounted magnet armature 09. The magnetic field exerts a magnetic force on the magnet armature 09 via an air gap between the pole core 07 and the magnet armature 09. Said magnetic force is transmitted via a pressure pin 11 of the magnet armature 09 to a piston of the central valve (not shown). The electromagnetic actuating unit is fastened by means of a flange 12 of the housing 08 to the central valve or to a housing surrounding the central valve. The magnetic field that can be generated by means of the coil 01 does not act entirely in the sliding direction of the magnet armature 09 on account of an eccentricity of the magnet armature 09. Said eccentricity is caused firstly by a degree of play of the magnet armature 09 and of the pressure pin 11 in the bearing arrangement thereof. Secondly, the eccentricity is a result of a deviation of the coaxiality between an armature bearing 13 and a pole core bearing 14. Said deviation may be extremely large depending on the assembly concept and on the tolerances of the components of the electromagnetic actuating unit. On account of the eccentricity of the magnet armature 09, parts of the magnetic field that can be generated by means of the coil 01 act laterally on the magnet armature 09, as a result of which forces are generated which act laterally on the magnet armature 09. Said laterally acting forces are proportional to the eccentricity of the magnet armature 09 or even proportional to the square of the eccentricity of the magnet armature 09. The alignment errors resulting from the deviation of the coaxiality between the armature bearing 13 and the pole core bearing 14 lead to tilting of the magnet armature 09 in its armature hearing 13. As a result of said tilting, the pressure pin 11 no longer slides on the entire bearing surface of the pole core bearing 14; in particular, a situation may arise in which the pressure pin 11 is mounted only on the edges of the pole core bearing 14. This leads to restricted functionality of the electromagnetic actuating unit and to increased wear of the pressure pin 11 and of the pole core bearing 14. Furthermore, the increased wear leads to an increasing eccentricity of the magnet armature 09, as a result of which the forces acting laterally on the magnet armature 09 increase yet further. As a result, the wear exhibits a progressive profile. The final result is failure of the device for variably adjusting the control times of the internal combustion engine, in particular on account of the fact that the adjustment of the control times of the internal combustion engine can no longer take place within the admissible adjustment times.
It is the object of the present invention, taking the electromagnetic actuating unit shown in FIG. 1 as a starting point, to provide an improved electromagnetic actuating unit which can firstly be produced particularly cost-effectively on account of larger possible tolerances of the individual components, and secondly has a long service life as a result of good concentricity of the bearing points.